As processors become more complex, the energy used by the processor increases and the need to maximize the energy usage becomes more important. In order to maximize processor energy efficiency, processor designs reduce the supply voltage (VDD) for applications with low-performance requirements (scaling). For example, register file circuits require a minimum operating VDD (VMIN) to successfully perform a write operation. Since register file arrays are distributed across a processor, the register file circuits and the processor logic share the same VDD. For this reason, the register file VMIN for a write operation limits the overall processor VDD scaling and the potential energy benefits. As shown in FIG. 1, the register file VMIN results from a contention path between the NFET transfer device (N4) attempting to bring node “T” to ground and the PFET pull-up device (P1) attempting to hold node “T” to VDD. Because the other NFET transfer device (N3) passes a weak “1” (VDD−Vt), where Vt is the transistor threshold voltage, into the complimentary node “C” and to the gate of P1, the P1 device stays partially on and resists the N4 device in bringing node “T” to ground. This contention is exacerbated as VDD reduces, especially when the process skews toward slow NFET devices and fast PFET devices. Since designs need to operate across all process corners, this contention limits the VMIN of register file circuits and consequently limits the processor energy efficiency. From simulations of a conventional processor, the register file VMIN results in a loss of more than 26% in processor energy savings.
Accordingly, there are long-felt industry needs for methods that improve upon conventional methods including the improved methods and apparatus provided hereby.
The inventive features that are characteristic of the teachings, together with further features and advantages, are better understood from the detailed description and the accompanying figures. Each of the figures is provided for the purpose of illustration and description only, and does not limit the present teachings.